T1053.002: At

Adversaries may abuse the at utility to perform task scheduling for initial or recurring execution of malicious code. The at utility exists as an executable within Windows, Linux, and macOS for scheduling tasks at a specified time and date. Although deprecated in favor of Scheduled Task's schtasks in Windows environments, using at requires that the Task Scheduler service be running, and the user to be logged on as a member of the local Administrators group.

On Linux and macOS, at may be invoked by the superuser as well as any users added to the at.allow file. If the at.allow file does not exist, the at.deny file is checked. Every username not listed in at.deny is allowed to invoke at. If the at.deny exists and is empty, global use of at is permitted. If neither file exists (which is often the baseline) only the superuser is allowed to use at.

Adversaries may use at to execute programs at system startup or on a scheduled basis for Persistence. at can also be abused to conduct remote Execution as part of Lateral Movement and/or to run a process under the context of a specified account (such as SYSTEM).

In Linux environments, adversaries may also abuse at to break out of restricted environments by using a task to spawn an interactive system shell or to run system commands. Similarly, at may also be used for Privilege Escalation if the binary is allowed to run as superuser via sudo.

Positive Technologies products that cover the technique

MaxPatrol SIEM knowledge base

mitre_attck_lateral_movement: PT-CR-211: Remote_Code_Execution_Via_AtSvc: Remote creation of a Windows scheduled task with AtSvc
mitre_attck_lateral_movement: PT-CR-2330: Subrule_Task_Created_via_Atsvc: A Windows scheduled task was created with AtSvc
hacking_tools: PT-CR-2332: Atexec_Activity: The AtExec tool designed to run commands using scheduled Windows tasks was used
unix_mitre_attck_persistence: PT-CR-1669: Unix_At_Job_Modify: A task was created with an AT command

Detection

ID	DS0022	Data source and component	File: File Modification	Description	On Windows, monitor Windows Task Scheduler stores in `%systemroot%\System32\Tasks` for change entries related to scheduled tasks, especially those that do not correlate with known software, patch cycles, etc. On Linux and macOS, all at jobs are stored in `/var/spool/cron/atjobs/`.

ID	DS0017	Data source and component	Command: Command Execution	Description	Monitor executed commands and arguments for actions that could be taken to create/modify tasks. Tasks may also be created through Windows system management tools such as Windows Management Instrumentation and PowerShell, so additional logging may need to be configured to gather the appropriate data.

ID	DS0003	Data source and component	Scheduled Job: Scheduled Job Creation	Description	Monitor for newly constructed scheduled jobs. If scheduled tasks are not used for persistence, then the adversary is likely to remove the task when the action is complete. On Windows, enable the "Microsoft-Windows-TaskScheduler/Operational" setting within the event logging service where several events will then be logged on scheduled task activity, including: Event ID 106 on Windows 7, Server 2008 R2 - Scheduled task registered Event ID 4698 on Windows 10, Server 2016 - Scheduled task created Event ID 4700 on Windows 10, Server 2016 - Scheduled task enabled Event ID 4701 on Windows 10, Server 2016 - Scheduled task disabled Tools such as Sysinternals Autoruns may also be used to detect system changes that could be attempts at persistence, including listing current scheduled tasks.

ID	DS0029	Data source and component	Network Traffic: Network Traffic Flow	Description	Monitor network data for uncommon data flows. Processes utilizing the network that do not normally have network communication or have never been seen before are suspicious. When AT.exe is used to remotely schedule tasks, Windows uses named pipes over SMB to communicate with the API on the remote machine. After authentication over SMB, the Named Pipe `ATSVC` is opened, over which the JobAdd function is called. On the remote host, the job files are created by the Task Scheduler and follow the convention `C:\Windows\System32\AT`. This pipe activity could be discovered with a network decoder, such as that in wireshark, that can inspect SMB traffic to identify the use of pipes. It could also be detected by looking for raw packet capture streams or from a custom sensor on the host that hooks the appropriate API functions. If no network or API level of visibility is possible, this traffic may inferred by looking at SMB connections over 445/tcp followed by the creation of files matching the pattern `C:\Windows\System32\AT\.` To detect AT via network traffic, a sensor is needed that has the ability to extract and decode PCAP information. Specifically, it needs to properly decode SMB and the functions that are implemented over it via NamedPipes. If a sensor meets these criteria, then the PCAP data needs to search for instances of the command JobAdd over the pipe ATSVC, which is all implemented over Windows SMB 445/tcp. Analytic 1 - Remotely Scheduled Tasks via AT source="Zeek:" (dest_port=445 AND proto_info.pipe="ATSVC") AND (proto_info.function="JobAdd")

ID	DS0009	Data source and component	Process: Process Creation	Description	Monitor for newly constructed processes with command-lines that create/modify or are executed from tasks. For example, on Windows tasks may spawn from `svchost.exe` or the Windows Task Scheduler `taskeng.exe` for older OS versions. Suspicious program execution through scheduled tasks may show up as outlier processes that have not been seen before when compared against historical data. Instances of the process at.exe running imply the querying or creation of tasks. Although the command_line is not essential for the analytic to run, it is critical when identifying the command that was scheduled. Analytic 1 - Scheduled Task `(source="WinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode="1") OR (source="WinEventLog:Security" EventCode="4688") Image="*at.exe"`

ID	Data source and component	Description
DS0022	File: File Modification	On Windows, monitor Windows Task Scheduler stores in `%systemroot%\System32\Tasks` for change entries related to scheduled tasks, especially those that do not correlate with known software, patch cycles, etc. On Linux and macOS, all at jobs are stored in `/var/spool/cron/atjobs/`.
DS0017	Command: Command Execution	Monitor executed commands and arguments for actions that could be taken to create/modify tasks. Tasks may also be created through Windows system management tools such as Windows Management Instrumentation and PowerShell, so additional logging may need to be configured to gather the appropriate data.
DS0003	Scheduled Job: Scheduled Job Creation	Monitor for newly constructed scheduled jobs. If scheduled tasks are not used for persistence, then the adversary is likely to remove the task when the action is complete. On Windows, enable the "Microsoft-Windows-TaskScheduler/Operational" setting within the event logging service where several events will then be logged on scheduled task activity, including: Event ID 106 on Windows 7, Server 2008 R2 - Scheduled task registered Event ID 4698 on Windows 10, Server 2016 - Scheduled task created Event ID 4700 on Windows 10, Server 2016 - Scheduled task enabled Event ID 4701 on Windows 10, Server 2016 - Scheduled task disabled Tools such as Sysinternals Autoruns may also be used to detect system changes that could be attempts at persistence, including listing current scheduled tasks.
DS0029	Network Traffic: Network Traffic Flow	Monitor network data for uncommon data flows. Processes utilizing the network that do not normally have network communication or have never been seen before are suspicious. When AT.exe is used to remotely schedule tasks, Windows uses named pipes over SMB to communicate with the API on the remote machine. After authentication over SMB, the Named Pipe `ATSVC` is opened, over which the JobAdd function is called. On the remote host, the job files are created by the Task Scheduler and follow the convention `C:\Windows\System32\AT`. This pipe activity could be discovered with a network decoder, such as that in wireshark, that can inspect SMB traffic to identify the use of pipes. It could also be detected by looking for raw packet capture streams or from a custom sensor on the host that hooks the appropriate API functions. If no network or API level of visibility is possible, this traffic may inferred by looking at SMB connections over 445/tcp followed by the creation of files matching the pattern `C:\Windows\System32\AT\.` To detect AT via network traffic, a sensor is needed that has the ability to extract and decode PCAP information. Specifically, it needs to properly decode SMB and the functions that are implemented over it via NamedPipes. If a sensor meets these criteria, then the PCAP data needs to search for instances of the command JobAdd over the pipe ATSVC, which is all implemented over Windows SMB 445/tcp. Analytic 1 - Remotely Scheduled Tasks via AT source="Zeek:" (dest_port=445 AND proto_info.pipe="ATSVC") AND (proto_info.function="JobAdd")
DS0009	Process: Process Creation	Monitor for newly constructed processes with command-lines that create/modify or are executed from tasks. For example, on Windows tasks may spawn from `svchost.exe` or the Windows Task Scheduler `taskeng.exe` for older OS versions. Suspicious program execution through scheduled tasks may show up as outlier processes that have not been seen before when compared against historical data. Instances of the process at.exe running imply the querying or creation of tasks. Although the command_line is not essential for the analytic to run, it is critical when identifying the command that was scheduled. Analytic 1 - Scheduled Task `(source="WinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode="1") OR (source="WinEventLog:Security" EventCode="4688") Image="*at.exe"`

Mitigation

ID	M1026	Name	Privileged Account Management	Description	Configure the Increase Scheduling Priority option to only allow the Administrators group the rights to schedule a priority process. This can be configured through GPO: Computer Configuration > [Policies] > Windows Settings > Security Settings > Local Policies > User Rights Assignment: Increase scheduling priority.

ID	M1028	Name	Operating System Configuration	Description	Configure settings for scheduled tasks to force tasks to run under the context of the authenticated account instead of allowing them to run as SYSTEM. The associated Registry key is located at `HKLM\SYSTEM\CurrentControlSet\Control\Lsa\SubmitControl`. The setting can be configured through GPO: Computer Configuration > [Policies] > Windows Settings > Security Settings > Local Policies > Security Options: Domain Controller: Allow server operators to schedule tasks, set to disabled.

ID	M1047	Name	Audit	Description	Toolkits like the PowerSploit framework contain PowerUp modules that can be used to explore systems for permission weaknesses in scheduled tasks that could be used to escalate privileges. Windows operating system also creates a registry key specifically associated with the creation of a scheduled task on the destination host at: Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\Tree\At1. In Linux and macOS environments, scheduled tasks using `at` can be audited locally, or through centrally collected logging, using syslog, or auditd events from the host.

ID	M1018	Name	User Account Management	Description	Limit privileges of user accounts and remediate Privilege Escalation vectors so only authorized administrators can create scheduled tasks on remote systems. In Linux environments, users account-level access to `at` can be managed using `at.allow` and `at.deny` files. Users listed in the at.allow are enabled to schedule actions using at, whereas users listed in at.deny file disabled from the utility.

ID	Name	Description
M1026	Privileged Account Management	Configure the Increase Scheduling Priority option to only allow the Administrators group the rights to schedule a priority process. This can be configured through GPO: Computer Configuration > [Policies] > Windows Settings > Security Settings > Local Policies > User Rights Assignment: Increase scheduling priority.
M1028	Operating System Configuration	Configure settings for scheduled tasks to force tasks to run under the context of the authenticated account instead of allowing them to run as SYSTEM. The associated Registry key is located at `HKLM\SYSTEM\CurrentControlSet\Control\Lsa\SubmitControl`. The setting can be configured through GPO: Computer Configuration > [Policies] > Windows Settings > Security Settings > Local Policies > Security Options: Domain Controller: Allow server operators to schedule tasks, set to disabled.
M1047	Audit	Toolkits like the PowerSploit framework contain PowerUp modules that can be used to explore systems for permission weaknesses in scheduled tasks that could be used to escalate privileges. Windows operating system also creates a registry key specifically associated with the creation of a scheduled task on the destination host at: Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\Tree\At1. In Linux and macOS environments, scheduled tasks using `at` can be audited locally, or through centrally collected logging, using syslog, or auditd events from the host.
M1018	User Account Management	Limit privileges of user accounts and remediate Privilege Escalation vectors so only authorized administrators can create scheduled tasks on remote systems. In Linux environments, users account-level access to `at` can be managed using `at.allow` and `at.deny` files. Users listed in the at.allow are enabled to schedule actions using at, whereas users listed in at.deny file disabled from the utility.